There has been a long search for materials for body protection against handgun projectiles for persons liable to face such dangers. Prior to the second World War the preferred armor material was steel, but using it for individual body protection is very impractical.
Research in this field was then directed toward the use of materials combining bullet-stopping properties with characteristics of pliability and lightness, so that they would be capable of giving users some degree of comfort. Thus it was that the research turned to the use of organic fibers in composite materials.
Polyamide fibers in particular are used in the manufacture of protective vests. Industrially, the fibers now involved are aramide fibers, including more particularly the phenyl-phthalamides, which are known commercially by the name of Kevlar.RTM.. These fibers offer high resistance to elongation and high tensile strength. Consequently, bullet-resistant armor is made of one or more layers of a closely-woven fabric made from these fibers. But it has been found that in use the superposition of several layers of this fabric results in the formation of wrinkles in which a bullet can become lodged. This defect is remedied by stitching these layers of aramide fibers to one another.
In general, the probability that a projectile will be stopped by a pliable protective material depends on the type of armor, the velocity of the projectile, as well as various other parameters such as the type of cartridge, the more or less dry or humid atmospheric conditions, etc. The result is that the body armor is generally designed to counter specific dangers, and is limited to a specific velocity range on the basis of armor standards and of the anticipated danger.